1. Field of the Invention
The present invention relates to a color correction method, a color correction device, and a color correction program for conducting color correction with respect to image signals by referring to a LUT. More particularly, the present invention relates to a color correction method and the like capable of reducing the color spacing of a LUT, while avoiding capacity increase of the memory that stores the LUT.
2. Description of the Related Art
A technology has been known by which, for example, a color of an image is beautifully displayed by conducting color correction with respect to TV video signals or image signals of digital cameras.
For example, a method for conducting color correction by using matrix computations (for example, see Japanese Patent No. 3611490, in particular FIG. 5 or Formula (1)) or a method for adjusting the lightness, saturation, and hue based on the maximum value, central value, and minimum value of the RGB signal (for example, see Japanese Patent Application Laid-Open No. 2003-163814, in particular FIG. 6) have been disclosed as the conventional technology of this type.
Furthermore, color correction is also conducted by using three-dimensional color tables. Color correction based on three-dimensional color tables was indicated to have high color reproducibility (for example, see the section relating to prior art in Japanese Patent No. 3611490), and the advantages of such color correction include good quality of displayed image and the capability of independently adjusting different colors.
Generally a three-dimensional color table stores the adjustment values of each component of an image signal (YUV, YCC, YCbCr, L*a*b, etc.) of a luminance—color difference system, but the values are stored discretely with consideration for memory capacity. The corrected image signal is then generated by conducting interpolation computations from the discrete values. The procedure described in Japanese Patent No. 3664364 is known as an interpolation computation procedure.
However, because errors occur during interpolation, the color table has to be configured with a spacing that is fine enough to maintain the image quality. On the other hand, the increase in memory capacity is also required to be prevented.
Accordingly, a technology has heretofore been disclosed (for example, Japanese Patent Application Laid-Open No. 2003-219194) by which a color space is used that was obtained by rotating the L*a*b* space through 45° about the lightness L* axis and then unequal spacing (nonlinear conversion) of coordinates thereof is created, thereby reducing the color spacing, while preventing the increase in memory capacity.
However, with the technology described in Japanese Patent Application Laid-Open No. 2003-219194, even though the rotated color space is used, there are values on the space that actually cannot be used. As a result, the memory utilization efficiency is not necessarily high. Therefore, the technology described in Japanese Patent Application Laid-open No. 2003-219194 does not necessarily prevent the increase in memory capacity.